(1) Technical Field
The present invention relates to a power generator. More specifically, the present invention relates to a solid oxide fuel cell encompassed by a spiral-wound heat exchanger and a method for forming the same.
(2) Description of Related Art
As the electronics industry's capability to manufacture small and powerful sensors, actuators, and functional devices increases, so does the demand for high-energy and/or power density microgenerators. Present-day lithium-ion batteries can deliver power densities on the order of 125 mW/cm3 (2000 mW/g) and thus often meet power density requirements of MicroElectroMechanical Systems (MEMS). However, energy densities of lithium-ion batteries, particularly when operated at the discharge rates required to obtain these power densities, are unacceptably low, and permit battery-powered microdevices to be operated only for limited periods of time. In contrast to lithium-ion batteries, which have energy densities of approximately 160 watt hours per kilogram (Wh/kg) or 350 watt hours per liter (Wh/l), liquid hydrocarbon fuels have exceptionally high energy densities, in the range of 10,000–15,000 watt hours per kilogram or 7,000–10,000 watt hours per liter. Thus, technologies which take advantage of inherently high energy densities of liquid hydrocarbon fuels are ideal for meeting increasing energy demands of the microelectronics industry. For example, a power generating device operating on propane and consisting of a fuel volume of fifty percent would only require a five percent fuel-to-electricity conversion efficiency to meet existing battery technology benchmarks. Such efficiency is easily achieved in a solid oxide fuel cell (“SOFC”). However, developing a SOFC for microelectronic applications presents several problems. Fabrication of micro-SOFCs is difficult and thermal management at such small-length scales is extremely challenging. SOFCs operate at temperatures of 300–1000 degrees Celsius, making their application in micro-devices problematic because of the difficulty overcoming the high rate of heat loss to the surroundings that occurs at such high temperatures in small devices. Therefore, the high rate of heat loss would make it difficult to generate heat at a rate faster than it is lost to the surroundings, which in turn would make it difficult to ignite fuel in the SOFC and generate a self-sustaining reaction.
Thus, a need exists in the art for a power generator that can be easily fabricated and can provide a high energy density and a sufficient degree of thermal management to reduce heat losses to a level whereby self-sustaining operation is possible, and whose size affords applicability in areas where space is limited.